The invention relates generally to an ink composition and more particularly to an ink composition which is solid or semi-solid at ambient temperature and jetted in a liquid state at elevated temperatures, the recording apparatus and method using them.
Ink jet recording is superior to other recording method because it is quiet and can print at high speed. Conventional ink compositions for ink jet recording include water based compositions. Recording is accomplished by allowing the ink to permeate into the recording paper. Unfortunately, the ink drop tends to blot as it permeates fully into the paper. Therefore, the edges of a recorded dot of ink is unclear and printing quality deteriorates.
Printing with water based ink compositions has other drawbacks. The print quality is affected by the type of recording paper being utilized so that the quality of printing from a particular recording apparatus can vary from poor to excellent depending on the type of paper on which printing occurs. In addition, conventional methods using water based liquid ink have not solved problems involving inadequately slow ink drying times. No prior art method has supplied consistent high print quality with fast drying times.
Liquid inks cause other problems relating to mechanical inadequacies of recording apparatuses. A low viscosity water based ink is normally stored in an ink tank and supplied through a tube to a print head which scans across the recording paper. The tube must have good flexibility and strength. Space within the recording apparatus must be reserved for tube movement. Leaks can develop within the supply system which is undesirable. When the ink supply tank is stored in the printing head, its rapid movement can form fine air bubbles within the ink which can cause problems such as cavitation within the ink head. Additionally, when an ink tank is replaced, ink tends to leak from the ink tank junction, and other areas, which can stain a users hands or clothing.
Ink jet recording methods for eliminating defects in water based inks are disclosed in U.S. Pat. Nos. 3,653,932, 3,715,219 4,390,369, 4,484,948 and 4,659,383 as well as Japanese laid open application nos. 55-54,368, 56-113,462 56-113,472 and 58-108,271. To print pursuant to the method described, a hot-melt ink composition which is solid at room temperature is heated so that it melts and the melted ink is propelled onto the recording paper. The ink then solidifies on the surface of the paper as it cools, to form a recorded dot.
When printing with a hot-melt ink composition, the print quality does not vary as much with paper type. However, hot-melt printing has disadvantages because ink dots protrude from the surface of the recording paper. Friction, heat or pressure can peel the ink off the recording paper and the ink will often stick to objects that contact the paper. Some of these problems have been solved by fixing the hot-melt ink to the recording paper with a reheating step heat which can be accompanied by pressure. However, the hot-melt ink tends to blot as the ink is dispersed into the recording medium during remelting.
Accordingly, it is desirable to develop an improved ink composition for ink jet printing and a recording apparatus and method which avoids these shortcomings of the prior art.